Ferroelectric bismuth-titanate nanoplatelets and nanowires with a new crystal structure

Abstract

Two different morphologies of ferroelectric bismuth titanate (Bi4Ti3O12) nanoparticles, i.e., nanoplatelets and nanowires, were synthesized by changing the concentration of NaOH during a hydrothermal treatment of precipitated Ti4+ and Bi3+...

Hydrothermal formation of bismuth-titanate nanoplatelets and nanowires: the role of metastable polymorphs

“…The hydrothermal method has proven to be a simple and versatile way to synthesise ferroelectric bismuthtitanate nanoparticles with a rich variety of different morphologies. [5][6][7][8][9][10][11][12][13][14][15][16] During the hydrothermal treatment of Bi and Ti hydroxides, bismuth titanate (BIT, Bi 4 Ti 3 O 12 ) forms at moderate concentrations of mineralizer hydroxide (NaOH or KOH), whereas at higher concentrations of the mineralizer a mixed, sodium/potassium bismuth titanate (Bi 0.5 IJNa/K) 0.5 TiO 3 ) perovskite is formed. 9,17 BIT is a promising, lead-free ferroelectric with a high Curie temperature (T C ∼ 675 °C), a modest spontaneous polarization ∼50 μC cm −2 and a high coercive field.…”

“…18 Apart from applications directly related to their ferroelectricity, BIT nanoparticles are also important in visiblelight photocatalysis, 8,11,19 electrocatalysis, 6 and piezocatalysis. 11,19 The hydrothermally synthesized BIT nanoparticles appear in a wide variety of different nanomorphologies, including 2-D platelet crystals, (i.e., rectangular nanoplatelets and nanosheets), [5][6][7]12,[14][15][16] 1-D crystals (e.g., nanowires, nanobelts, nanobundles, nanorods), 6,7,13,16 and 3-D nanostructures assembled from 1-D or 2-D nanoparticles. [8][9][10][11]13,14 The morphology of the formed nanoparticles can be controlled to a large extent by selecting the experimental conditions during the hydrothermal synthesis, e.g.…”

“…, the type and concentration of the mineralizer, the source of titania, the reactant concentrations, the reaction temperature and time, and the use of different surfactants. 6,7,13,15,16 There were several attempts to explain the mechanisms leading to different morphologies, mainly based on the adsorption of the mineralizer cations (Na + , K + ) on the surfaces of the growing particles 9,13 or templated growth involving layered titanates (K 2 Ti 6 O 13 , Na 2 Ti 3 O 7 ) as the templates. 10,15,20 In our previous paper 16 we revealed that the diverse morphologies of bismuth-titanate nanostructures are related to the different crystalline structures of the formed nanoparticles.…”

“…6,7,13,15,16 There were several attempts to explain the mechanisms leading to different morphologies, mainly based on the adsorption of the mineralizer cations (Na + , K + ) on the surfaces of the growing particles 9,13 or templated growth involving layered titanates (K 2 Ti 6 O 13 , Na 2 Ti 3 O 7 ) as the templates. 10,15,20 In our previous paper 16 we revealed that the diverse morphologies of bismuth-titanate nanostructures are related to the different crystalline structures of the formed nanoparticles. In bulk form BIT crystallizes in an Aurivillius layered structure, which is characterized by two structural layers, i.e., a (Bi 2 O 2 ) 2+ layer and a perovskite (Bi 2 Ti 3 O 10 ) 2− layer, alternating along the pseudo-tetragonal c-axis.…”

“…Atomic-resolution, high-angle annular dark-field imaging with a C S -probe-corrected scanning-transmission electron microscope showed the cation arrangement in two structural layers alternating along the orthorhombic c-direction: a structural layer that resembles the (Bi 2 O 2 ) 2+ layer of the Aurivillius-type structures, and a structural layer composed of two parallel layers of the Ti atoms, where every sixth Ti is replaced by Bi. 16 In this investigation we systematically analysed the evolution of different crystalline structures/morphologies during the hydrothermal synthesis of BIT. The aim was to reveal the mechanisms involved in the formation of different nanostructures with special attention to the role of metastable polymorphs which appear as the transient phases.…”